The sky is big. Searching it for potentially hazard objects like asteroids and comets is hard. The best way to do it? A big ‘scope, equipped with a BIG camera, and a wide, wide field of view. That’s just what the Panoramic Survey Telescope & Rapid Response System — PanSTARRS — brings to the table. It’s just a prototype, but it has a 1.8 meter ‘scope on — wait for it, wait for it — Mount Haleakala, and it sports a 1.4 gigapixel camera. You read that right: 1.4 billion pixels.

It scans the skies looking for threatening objects, and astronomers just announced they have found their first one: 2010 ST3, an asteroid 50 meters (150 feet or so) across. It was found September 16, when it was still 30+ million kilometers (20 million miles) from Earth. Here’s the object in question:

How big a threat is this object? Well, not very: there’s "a very slight chance" it will hit Earth in 2098, so I’m not terribly concerned. When astronomers map an orbit of an object, there’s some uncertainty in the measurements. It’s hard to get the exact position of the object, and its motion over a day or two isn’t enough to get a good idea of its trajectory. The farther you try to project where it’ll be in the future, the fuzzier the prediction gets.

For something like 2010 ST3, there’s a huge volume of potential space it might occupy come 2098, and it so happens that the Earth is in that same volume of space at that time. But the Earth is near the edge of the projected position, and as time goes on, and the orbit is better determined, the volume of space the asteroid might be in will shrink. Eventually, what almost always happens is that the Earth winds up outside that volume as our data get better. That’s why the odds of it hitting us are so low.

Now, if it did hit us, it would be bad. An object a bit smaller than that carved out Meteor Crater in Arizona, a hole over 1.5 kilometers across (that’s me posing in front of it; click it to get an idea of how big this scar is, and bear in mind the far rim is almost a mile away). An impact by something like that is about the same as exploding a 20 megaton bomb.

So yeah, bad.

The good news here… let me correct myself: the great news here is that Pan-STARRS found this thing at all! From that distance, an object this small is really hard to see, and no other asteroid survey could’ve found it. That means that as time goes on, Pan-STARRS will find lots and lots of threatening objects. And they’re out there whether we look for them or not! So it’s best to find the beasties before they find us.

And when we do find them, we need to keep a really good eye on them. We need accurate orbits, and good statistics, so that we can figure out just how big a threat these guys are. 2010 ST3 is almost certainly benign, at least for the next century. But there are thousands more like it roaming the sky. We don’t get hit very often, but we do get hit.

For those of you who fret about such things, I like to say that this is something to be concerned about, but not something to worry about. Worry accomplishes nothing, but concern means we’re turning our brains to the problem. And that’s the very best way to solve problems.

I’m glad that you are reporting of stuff like this. I often hear stories that say “Scientists breathed relief as there was a chance X might of hit us but didn’t” and I always then think: why do I never hear about this stuff until after the fact?

Assuming, for the sake of argument, that it did hit us (be it surface impact or airburst), the odds of it actually happening over inhabited territory are maybe 1 in 5, perhaps, since the Earth is 70% covered in oceans and large parts of the other 30% are uninhabited (the Sahara, Siberia, northern Canada, Greenland, the Australian outback, Antarctica etc). So, even it our paths do cross one the size of an olympic swimming pool, the probability that it does any damage or it causes any injuries is quite low.

I kinda WANT to have something this size hit us within my lifetime (safely in an out of the way place, of course). Imagine the science that could be done on a crater only hours or days old! We’d learn an incredible amount. And if we had a fair warning, we could set up HD video coverage, an array of sensors, etc… It would be amazing!

I kinda WANT to have something this size hit us within my lifetime (safely in an out of the way place, of course). Imagine the science that could be done on a crater only hours or days old! We’d learn an incredible amount. And if we had a fair warning, we could set up HD video coverage, an array of sensors, etc… It would be amazing!

Well there was the one that hit the Sudan – & was discovered and tracked down to the ground beforehand – last year if memory serves.

I wonder how this rock compares with that one?

Also wondering – is this 2010 ST3 bolide candidate now getting too small to be properly termed an asteroid and better described as a meteroid or something instead?

It’s odd that is has such destructive power. 50m doesn’t really sound like much, does it? If push comes to shove, would nuclear weapons suffice to blast it to smaller, less threatening fragments? It’s size implies that nukes might be enough, but I think hollywood has really screwed me up, so I don’t want to hazard any guesses.

EvanT: the reason it has so much destructive power is that it is moving very fast relative to the Earth. Kinetic energy is proportional to the mass of an object, and proportional to the square of its velocity.

When an impactor hits, it scrubs off all that kinetic energy in one go, hence the big explosion.

@TCs (#2), while an impact may not cause a lot of direct deaths and destruction if it hit in the middle of the Pacific for instance, there are secondary effects. Tsunamis (Christmas 2004?). Atmospheric dust (Iceland volcano 2010). And of course all the associated effects on the food chain, global weather, etc. It’s not just the big boom that one needs to worry about.

Thanx ! Local newspapers printed an article about it .. but the totally omitted all information from it ! No name, size, date, or observer. Only that the observer was ‘new’, and that the asteroid might hit us.

I’m not too concerned about it either. Mostly because I’ll be 113 years old if it hits, and if we haven’t destroyed ourselves by then, we should have had enough time to put together an evacuation plan for the affected area and set up lots of cameras to catch the cool explosion.

It’s odd that is has such destructive power. 50m doesn’t really sound like much, does it? If push comes to shove, would nuclear weapons suffice to blast it to smaller, less threatening fragments? It’s size implies that nukes might be enough, but I think hollywood has really screwed me up, so I don’t want to hazard any guesses.

Yeah, what Mark W (10) said, plus…

Assuming it to be spherical (it won’t be, but I can’t do the maths if it isn’t), its volume will be c. 65,000 m3. Assuming its density is about 3 g/cm3 (i.e. a dens-ish gravel), its mass will therefore be almost 200,000 tonnes.

If it were to hit, a likely relative velocity is in the vicinity of 30 km/s, so its kinetic energy will be:
Convert to SI gives 2 x 108 kg and 3 x 104 m/s, and KE is 1/2 m x v2, giving 1.8 x 1017 Joules, which is plenty (by way of comparison, a single kilowatt-hour is 3.6 MJ).

That energy will be delivered onto the Earth whether it hits as a single lump or as a cloud of gravel.

Assuming, for the sake of argument, that it did hit us (be it surface impact or airburst), the odds of it actually happening over inhabited territory are maybe 1 in 5, perhaps, […] So, even it our paths do cross one the size of an olympic swimming pool, the probability that it does any damage or it causes any injuries is quite low.

You are assuming that the only damage is a 1-mile-wide crater where it hits.

Suppose it were to hit the Indian Ocean. Imagine the tsunami it would cause, and what would happen to that part of the world. Or that Atlantic Ocean, and the damage that that tsunami would cause. (Not to mention the rest of the world, too. We’re not talking about a rock tossed into a pond.)

Or perhaps the middle of the Sahara. It’s not just a big hole in a bunch of sand. All the debris that would be kicked up into the atmosphere would probably encircle the globe. Consider the damage caused by Mount Saint Helens, or whatever-its-name-is volcano in Iceland.

From that distance, an object this small is really hard to see, and no other asteroid survey could’ve found it

I’m actually gonna disagree here. Although PS1 is a great step forward, the object was discovered at around V22, and both Mt. Lemmon (G96) and Spacewatch (291) are capable of detecting objects this faint (G96 does on regular basis). The main advantage of PAN-STARRS (esp. once all four scopes are up and running), besides the ability to reach beyond V23, is the field of view, i.e. it’s capable of scanning the entire sky visible from Hawaii a few times in a month – G96 can scan only +/- a few degrees around the ecliptic if they want a thorough coverage within a single Lunation.

For something like 2010 ST3, there’s a huge volume of potential space it might occupy come 2098, and it so happens that the Earth is in that same volume of space at that time.

I know this comes from the University of Hawaii release, but it really sounds like a cheap attempt to get a bit more attention in the press. The object has been observed only on two nights and has an arc of 43 hours. If not observed again within the next 2-3 weeks after which the object will be too faint, the current orbital elements will not be good enough for direct recovery during the next opposition not to mention predicting its position to within 10’s of lunar distances in 2098. The minor planets community knows better!

The worst thing it could do to anybody alive today is shake up our dead bones in 88 years… (unless someone invents a pill so that we can all live to be 150).

Suppose that we need to do something about an asteroid headed for Earth someday. Isn’t it a risk that many people will think “I don’t want to pay extra taxes / spend any effort to divert this thing, because it’s so far in the future that I don’t need to think about it”? Before they know it, it’s too late and a disaster is unavoidable…

Think about a bullet, consider its size and mass and the kind of damage it can do. If it’s not an explosive round, then all that damage is from the kinetic energy imparted to itwhen it is fired from the gun.

hey, even if it hits it will be “as a 20 megaton bomb”. We detonated way larger ones (Tsar Bomb was 50, IIRC), admittedly in the atmosphere. But it’s not as if *one* 20 megaton hit would trigger next ice age, destroy half of coastal regions worldwide etc as some of you seem to think. Bad, yes, but not devastating. At least if it does not hit some megalopolis directly. And even then… some no-flight days, perhaps a (slight) recession. Some strange weather phenomena. And perhaps a 7-digit number of deaths.

Pan STARRS will be doing lots of other great science too, not just looking for near earth objects. Just one example: when they have all four of its scopes up, it will be capable of finding Jupiter-sized planets out to 2000 AU, (and Neptune, Earth, and Mars-sized objects somewhat closer in, but still well beyond current detection limits).

“Looking at the two images, any idea what causes the dark spots? Are they areas of failed pixels in the imaging array? ***Or perhaps something more interesting?”***

Well, it’s complicated. The blacked out spots are hiding images of angels flying around the solar system (herding the asteroids away from the Earth, I’m sure). If you were allowed to see them, then you would have proof of them and would no longer need faith to believe. While this may seem like a good thing, conspiracy theorists and troublemakers would quickly claim that those are false images of angels, trotting out all sorts of Photoshoppy-type proof, and this would lead people to stop believing in them even though they are in fact real. BUT! If you only believe in something that doesn’t actually seem to be there, and is seemingly invisible, then no one can prove to you that they are not there. Angels = 1, Satan = 0.

Thanks for the replies people. I’m fairly physics literate myself so I realize the issues.

The real question is, which is worse for humans: disintegrating the asteroid and having the kinetic energy pumped into the atmosphere as thermal energy (how much would 1.8 x 10^17 J raise atmospheric temperature?), a ground impact (and the ejecta that comes along with it) or an ocean impact (and the accompanying tsunami)? Any ideas?

I suspect that almost any ocean hit would be bad. Very bad indeed. People focus on an impact in a city but that’s relatively unlikely. Since the world is 2/3 ocean that’s what we need to worry about (and avoid).

large amounts of energy in the atmosphere we have experience with: nothing happends very much. (Except very near to the explosion, of course). See http://en.wikipedia.org/wiki/Tsar_Bomba
50 Megatons would be 2.5 times the energy released of this asteroid, and it was released nearly entirely in the atmosphere (some sources say the fireball touched the ground). Third degree burns would have been the result for up to 100 km, but that’s mostly it. Remember that these effects are greatly depending on the energy of the explosion.
We even have experience with ground explosions of this magnitude: http://en.wikipedia.org/wiki/Castle_Bravo
Castle Bravo was 15-22MT yield and the only effects far away worth mentionioning came from the radioactive fallout (something most likely not to be found in that abundance when an asteroid explodes).
On the other hand an asteroid would probably release earth quakes and such, so of course those are not easily comparable, but we already *have* some (limited) experience. All in uninhabited area, of course. If the asteroid hits directly (near) a large city the effects on that city would be devastating – as would be a nuclear bomb detonating there…
The probability of that asteroid hitting such an area is quite small, on the other hand.

Great article, but the thing I found truly amusing was the advertisement saying ‘Keep David Vitter’ that appeared just below the article, and a link to some weird Close Combat training course right above it. If being able to identify threats is the first step to dealing with them . . .
*¬◊

“Now, if it did hit us, it would be bad. An object a bit smaller than that carved out Meteor Crater in Arizona, a hole over 1.5 kilometers across”

Is he taking into account the ablation that would take place as it passed through the atmosphere? In other words, is this an apples to apples comparison? Do we know how large the Arizona meteoroid was in space, and how much mass it lost before hitting the ground? If we don’t know, the comparison would seem to be spurious.

As I recall, the first Nuc test in New Mexico vaporized a chunk of desert floor about a quarter mile in diameter.

Well, yes and no.

Yes, it made a crater, but the steel reinforcement of the Trinity tower footings remained unvaporised, so the crater was pretty shallow.

Bear in mind that, although we compare bolide impacts to nuclear explosions, the analogy is limited. All of the energy of the nuke comes out as radiation of one sort or another, which heats the air and creates a shock wave. The energy of an impacting bolide is kinetic, so the situation is a little different. Yes, heat is generated, but as a by-product of the physical impact. So I’m not sure the crater formation is directly parallel.

The real question is, which is worse for humans: disintegrating the asteroid and having the kinetic energy pumped into the atmosphere as thermal energy (how much would 1.8 x 10^17 J raise atmospheric temperature?), a ground impact (and the ejecta that comes along with it) or an ocean impact (and the accompanying tsunami)? Any ideas?

Erm … well, you’re getting into some pretty detailed calcs there.

For instance, if you look up the specific heat capacity of air and the mass of our atmosphere, you can work out an average increase in atmospheric temp if the energy is all dumped into the atmosphere. But I know almost nothing of fluid dynamics so I have no idea how the heat would actually be distributed if this were to be the case.

In terms of a ground impact, the effects would largely depend on what kind of ground it hit – how deep the soil, what kind of bedrock, that kind of stuff. And, again, to answer your question requires getting stuck into an awful lot of detail, and those calcs are outside my areas of knowledge (i.e. I don’t know how to go about calculating the effects of a ground strike).

As for a tsunami impact, IIUC the effects depend on the angle of impact and the depth of the water (depeer water = bigger tsunami, again IIUC). However, by way of comparison, an article in New Scientist about 4 or 5 years ago described a mountainside on one of the Canary islands that is geologically unstable, and if it falls into the Atlantic it would wipe out most of the eastern seaboard of the USA. More mass there than this rock, but far less energy, so I don’t know how useful the parallel is.

Being able to see something 150 feet across from 20 million miles away is a much-needed boost to the still-underappreciated but vital field of NEO detection. Technology like this could save millions of lives someday, by giving people enough time to evacuate a city in the event a small NEO is found to be on a collision course with the city or nearby offshore. Is this the only Pan-STARRS system? If so, there need to be more.

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